If you have not created the Firebase project check here

Enable phone Authentication:

Update SHA certificate fingerprints to your Firebase Android App:

• If you manage your app signing and are in development mode, you can check here to find your SHA certificate
• If you enable Google to play to manage your app signing check here to get SHA certificate

We prefer to Google manage your app singing then after uploading your app to Google play you can get it there.

Don’t forget to download and replace the latest google-services.json again

Replace google-services.json again after updated SHA1 to anvoid recapcha when user click to button login.